I have to think about that one a bit. I've only heard of such things
but never seen one. It leaves me very curious since lens tubes both
expand and shrink with temperature. If there is sufficient linear
expansion to cause focusing error when the tube shrinks with cooling
temperature there is also sufficient change in length to cause focusing
error when the tube expands with temperature.
The "past infinity" would occur with a shrinking tube but a "short of
infinity" would occur with an expanding tube. It seems to me both
situations are equally likely but I've never hear of a tube marked for
both nor one with specific temperature recommendations.
Does anyone have an actual lens so marked and with instructions how to
use it?
Chuck Norcutt
On 11/6/2014 8:15 PM, Moose wrote:
Nope.
Or at least not necessarily. As I understood it, the 'focus past
infinity' and the infinity mark with a line attached to the bottom of it
on some lenses both exist to deal with changes of focus with temperature
changes.
Should that be true of Brian's lens, an infinity mark made in warm day
will likely be inaccurate in cool night.
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